One of the basic and recurring problems in the present day electronic industry involves the dissipation of heat from highly concentrated pin grid arrays packaged rather densely on printed circuit boards.
The generally known means for dissipating the heat generated in these concentrated spatial areas is by the attachment of heat sinks to the pin grid array package. There are presently two basic methods whereby heat sinks are attached to a pin grid array package in the present art. These methods are (1) to solder a heat sink to the metalized surface of a pin grid array package, and (2) to attach a heat sink with an adhesive paste or fluid).
There are some major disadvantages in each of these presently used methods.
Those heat sinks that are soldered to the pin grid array package are generally required to have relatively small contact area between the package and the heat sink. This is due to the thermal coefficient of expansion of the different materials used and which are thus mismatched in their coefficient of expansion. For example, the normal materials which are used such as beryllium oxide, and copper, or aluminum, each have a different coefficient of expansion. However, this requirement of a small contact area operates to limit the conduction path for heat to be transferred over to the heat sink.
When a heat sink is attached by means of adhesive paste or adhesive solutions, the thermal expansion mismatch problem is generally eliminated. However, there is a disadvantage to the adhesives in that they are considered to be unreliable in certain circumstances and when a failure occurs, the failure of the heat sink will cause failure of the integrated circuits and thus present a considerable risk to the integrated circuit and surrounding circuitry when adhesives are used as a means of heat sink attachment.
For example, a varying number of heat cycles or a number of thermal shocks or a number of actual physical shocks may operated to break or disconnect the adhesive solution and thus prevent the heat sink from having sufficient contact to dissipate the heat, causing the loss of the integrated circuits.
With the basic consideration that a mechanical system of holding the heat sink to a chip is much more reliable than either solder or adhesive connection, it was felt possible to design and build an unusually large conduction path without incurring the thermal expansion mismatch problem. Further, the mechanical connection also permits an adjustable pressure to be developed between the heat sink and the pin grid package which can also be helpful to improve the heat transfer factors. Accordingly, the presently described heat sink configuration was developed to overcome the limitations of previous methods of attaching heat sinks to a pin grid array.